<!DOCTYPE html>
<html lang="zh">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .box1{
            width: 0;
            height: 0;
            border-bottom:10px red solid;
            border-left:10px transparent solid;
            border-right:10px transparent solid;
            /*border-color: red #bfa orange yellowgreen;*/
        }
    </style>
</head>
<body>
<div class="box1"></div>
</body>
</html>